1. Field of the Invention
The present general inventive concept relates to a hard disk drive apparatus, a method to control flying height (FH) of a magnetic head of the hard disk drive apparatus, and recording media for a computer program to perform the method, and more particularly, to a hard disk drive apparatus that can actively control the FH of a magnetic head, a method to control the FH of a magnetic head of the hard disk drive apparatus, and recording media for a computer program to perform the method.
2. Description of the Related Art
Hard disk drive apparatus (HDDs) formed of electronic parts and mechanical parts are memory devices to record and reproduce data by converting digital electric pulses to a magnetic field that is more permanent. The HDDs are widely used as auxiliary memory devices of computer systems because of fast access time to a large amount of data.
With the recent increase in TPI (tracks per inch; a density in a radial direction of a disk) and BPI (bits per inch; a density in a rotational direction of a disk), the HDD has achieved a high capacity and its application field has expanded. Accordingly, there has been a request for development of compact HDDs that can be used for portable electronic products such as notebooks, personal digital assistants (PDAs), and mobile phones. HDDs having a diameter of 2.5 inches are already developed and applied to notebook computers. Compact HDDs having a diameter of 0.85 inches, which are as small as a coin, have been recently developed and are expected to be used for mobile phones or MP3 players in the future.
As the capacity of the HDD increases, the size of a read/write sensor of a magnetic head decreases and a flying height (FH) of the magnetic head that is lifted over a recording surface of a disk gradually decreases. That is, when a high TPI and a high BPI are realized to manufacture a high capacity HDD, the width of a track decreases. When the track width decreases, a strength of a magnetic field becomes weak accordingly. Thus, writing data to the recording surface of the disk or reproducing data from the recording surface of the disk is not smoothly performed.
For this reason, methods of effectively reducing an interval between the disk and the magnetic head, that is, reducing the FH of the magnetic head with respect to the disk, have been and are actively being developed as a condition precedent to improve the read/write performance of the magnetic head with respect to the disk. One of the methods is to reduce dispersion of the FH of the magnetic head and another method is to effectively control the FH to obtain the minimum FH of the magnetic head.
FIG. 1 illustrates changes in a FH of a magnetic head according to temperature changes in an HDD according to a conventional technology. FIG. 2 is a graph illustrating in non-dimension the FH of a magnetic head according to the measured temperature in the HDD of FIG. 1. Recently, the FH of a magnetic head 141 is measured using a flying on demand (FOD) apparatus in a burn-in process. An FOD voltage is selected to maintain the magnetic head 141 at a desired FH in a user environment.
In detail, when an FOD voltage that gradually increases is applied to the magnetic head 141 through a touchdown test in the burn-in process, the magnetic head 141 lifted and maintained at a predetermined height is lowered toward a disk 111 and then contacts the disk 111. A reference FOD voltage profile indicating a relationship between the FOD voltage and the FH of the magnetic head 141 through the touchdown test is provided.
An FOD voltage needed for a target clearance, that is, a target FH, in an actual user environment is produced from the reference FOD voltage profile. Related data is stored in a maintenance cylinder of the disk 111. Thus, the FOD voltage produced in the burn-in process is applied to a heater (not illustrated) included in the magnetic head 141 in the user environment so that the target FH of the magnetic head 141 is maintained.
However, in the conventional method for controlling the FH of the magnetic head 141 of the hard disk drive apparatus, it is a problem that a measured value is used in the burn-in process, in particular, in an actual user environment without considering the change in the FH according to the temperature. Accordingly, the FH of the magnetic head 141 in the burn-in process may be a value in a normal condition, that is, at room temperature. When during the burn-in process conditions where the temperature when the FH of the magnetic head 141 is measured is the room temperature and the magnetic head 141 flies at the original FH are satisfied, the FOD voltage to set the target FH in the user environment is selected based on the FH of the magnetic head 141. However, although external environment conditions are controlled in the burn-in process, in practice the temperatures of all hard disk drives cannot be equally maintained due to various limits.
In general, as illustrated in FIGS. 1 and 2, in an environment in which the temperature is higher than at room temperature, the FH of the magnetic head 141 is lower than that in the room temperature. In an environment in which temperature is lower than the room temperature, the FH of the magnetic head 141 is higher than that at room temperature. That is, even in the burn-in process, the measurement operation can be carried out at a temperature condition different from room temperature. When the measurement is made in such a condition, the FH of the magnetic head 141 can be mis-measured. Accordingly, an incorrect FOD voltage is selected in the user environment. When the mis-measured FOD voltage due to the incorrect temperature is applied to the magnetic head 141 to control the FH of the magnetic head 141, various problems can be generated.
Referring to (B) and (C) of FIG. 1, when the burn-in process is performed in the higher temperature environment, FH2 of the magnetic head 141 is measured to be lower than FH1 of the magnetic head 141 at the room temperature and a lower FOD voltage is selected for the target FH in a user environment. Then, when the temperature in an actual user environment is lower than the high temperature environment, the FH of the magnetic head 141 is maintained at a position higher than the target FH. As a result, a reliability problem such as weak write can be generated.
Also, referring to (A) and (B) of FIG. 1, when the burn-in process is preformed in the lower temperature environment, FH3 of the magnetic head 141 is measured to be higher than the FH1 of the magnetic head 141 at the room temperature and a higher FOD voltage is selected for the target FH in a user environment. Then, when the temperature in an actual user environment is higher than the high temperature environment, the FH of the magnetic head 141 is maintained at a position lower than the target FH. As a result, a head disk interference (HDI) where the magnetic head 141 and the disk 111 collide with each other can be generated.
That is, when the burn-in process is performed not at the room temperature but at a temperature higher or lower than the room temperature, the FH of the magnetic head 141 can be incorrectly measured. Accordingly, in the actual user environment, since the incorrectly measured FOD voltage is applied due to the effect of the temperature, the weak write or HDI can be generated.